321.314  When signal required.
  No person shall turn a vehicle from a direct course upon a highway unless and until such movement can be made with reasonable safety and then only after giving a clearly audible signal by sounding the horn if any pedestrian may be affected by such movement or after giving an appropriate signal in the manner hereinafter provided in the event any other vehicle may be affected by such movement.
[S13, §1571-m18; C24, 27, 31, 35, §5032; C39, §5025.04; C46, 50, 54, 58, 62, 66, 71, 73, 75, 77, 79, 81, §321.314]
For applicable scheduled fine, see §805.8A, subsection 6